Optimistic Rollup
A Layer-2 system that assumes state transitions are valid unless challenged with a fraud proof.
Explain Like I'm 12
A Layer-2 system that assumes state transitions are valid unless challenged with a fraud proof.
Why It Matters
Scaling concepts explain how blockchain systems increase capacity while balancing security and decentralization.
How It Works
Transactions are collected by a sequencer and published to Ethereum as call data. For a set time, anyone can submit a 'fraud proof' if they notice an error in the batch. If challenged, the protocol executes the specific transaction on-chain to determine the correct state, and the incorrect entry is discarded.
Real-World Example
Optimism and Arbitrum are both major implementations of Optimistic Rollups on the Ethereum network.
Advantages
- High throughput and low fees
- Security rooted in Ethereum
- Relatively simple to implement
Limitations
- Significant wait times for fund withdrawals
- Relies on honest participants to challenge fraud
- Centralized sequencers create single points of failure
Common Misconceptions
- Many believe rollups are insecure because they are off-chain; they are actually as secure as the main chain if a validator is active.
- Some think transactions are instant, but they are only finalized on mainnet after the challenge period.
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Related Terms
Data Availability
The property that transaction and state-transition data needed to verify a blockchain or rollup is accessible to participants.
Layer 2
Layer 2 refers to secondary protocols built on top of an existing Layer 1 blockchain to improve scalability, efficiency, and speed. These solutions move the bulk of transaction processing off the main chain, while still inheriting the security and finality provided by the base Layer 1. By batching transactions or using alternative data availability paths, Layer 2 networks reduce congestion and transaction costs on the main ledger, facilitating wider mainstream adoption of decentralized applications.
Rollup
A Rollup is a Layer 2 scaling solution that increases Ethereum's transaction throughput by processing transactions off-chain and then posting the compressed data to the Ethereum mainnet. By handling the heavy lifting of computation externally and only using the mainnet for data availability and settlement, rollups drastically reduce gas fees and increase transaction speed while inheriting the security properties of the Ethereum base layer.
Rollup
A rollup is a scaling technique that moves computation and state storage off the main blockchain (Layer 1). It 'rolls up' hundreds or thousands of transactions into a single batch, generating a cryptographic summary that is posted back to the main chain. This drastically reduces the data requirements on the main network while ensuring that the validity of the bundled transactions can be audited and verified by anyone, maintaining the decentralization of the parent chain.
Throughput
The amount of transaction or computational activity a blockchain can process over a given period.